It is proposed to further investigate the regulation of leucine biosynthesis in enteric bacteria, with emphasis on the role of the first specific enzyme of the pathway, alpha-isopropylmalate synthase. Plans include the study of possible specific interactions between this enzyme and one or more isoaccepting species of leucine tRNA. Leucine pathway regulation will also be studied in yeast, in order to compare the bacterial system with that of a more highly developed, eucaryotic organism. The mechanism and possible physiological significance of the recently discovered coenzyme A-mediated inactivation of yeast alpha-isopropylmalate synthase will be looked at more closely. BIBLIOGRAPHIC REFERENCE: J.W. Tracy and G.B. Kohlhaw, "Reversible, Coenzyme A-Mediated Inactivation of Biosynthetic Condensing Enzymes in Yeast - A Possible Regulatory Mechanism", Proc. Ntl. Acad. Sci. (US) 72, 1802 (1975).